XT 550 ignition problems HELP

Still not given up on the XT 550 ignition and carb issues

So since last time when I had the bike running on an old MT 50 CDI unit. The new CDI unit arrived and I thought this would be the end of the story (now a new cdi and a ht coil)

But oh no !

I fitted the new CDI all corresponding wires connected orange to coil ,black to earth ,brown to brown and red to red to the generator .

Red and White, and green and white

, and green to the pulsar

now no spark at all , DEAD AS A DOOR NAIL ??????? put the MT 50 CDI back on and a spark comes back !

Now I'm confused

The left cover off again and check out the resistance measure, check for damage, missing bits and all seems ok !!!!????

WHY will the bike spark with a MT 50 CDI but not the new XT. 550 cdi

Please help before I loose my marbles !!

You can find all you need on Adv Rider.

Thanks for the reply I will have a look and see what I can find

In the mean time a few more questions to try to narrow down the issue.

Having confirmed the resistance readings on the brown and red wire and the green / white / red / white etc i am wondering on this bike if the spark is generated by the power sent down the red wire and the brown wire or is it generated from the green and white / red and white / and the green

Or is it a mixture of all of the above

I am wondering if the MT 50 CDI works as it is using power from the red wire and the brown wire only and then perhaps the XT CDI wants power from only the (red and white / green and white / and green )

bearing in mind this engine is in a moto x bike frame so has only the ignition circuits present

Any one know ?

I know the ignition has an advance timing capability but I don't know how it works re wiring / power etc

Any help would be appreciated thanks w



The XT550 had an unusual advance system....the pick-up coil is actually 2 coils.  At low speed and idle  the CDI used the pulse from the pickup coil at 12 degrees advance and as the bike rpm increased the second pick-up coil (+30 degrees advance I believe) started to drive the CDI.   A common problem with XT550's is the pick-up coil being burnt out on one side or the other.   If the coil is burnt out on one side and you happened to hook the normal CDI to a good side you could get a spark, and the bike might start and idle (if it happened to be the low-speed winding that was good), but there would be no advance.


The wires from the pulser (pickup) are green (center of coil ground)  red/white and green/white.  check for a very small resistance reading from the  red/white to green....and then from the green/white to green.  If one is open, that's your problem.  The manual has a method for testing the pickup.


just a guess...



hey thanks for the idea

The pulsar wires all check out to the spec in the manual bang in the middle of the range .

the resistance between red and brown wires also checks out

BUT with the MT50 cdi in the bike will idle and rev to about 1/4 throttle until it blurs and does not rev properly

In conclusion if the pick up coils are bad would there be enough juice to get the mt50 cdi to spark at low revs but not enough to fire the xt. Cdi at all ? I dunno

The original Yam CDI has circuitry in it to select from the two advance pulses.  A normal CDI doesn't and will only run at 12 degrees BTDC and without more advance it can't handle faster RPM.   But having proof the bike runs on the MT50 cdi that means the everything except the CDI is working and the new XT550 cdi might be hooked up wrong.  There is no easy test for the yam CDI and all I can suggest is checking the wiring.


Here is a webpage where a homemade CDI for your system was constructed successfully.  There are diagrams etc. that might help with the wiring and explain the theory.




I had my XT550 running on a home made 12 degree only CDI at highway speed.  (by a friend, don't ask me, I can't solder worth crap)  To be perfectly honest, I didn't notice any difference.

IMHO, if it runs on the MT50 CDI, just leave it and try to get your money back on the other CDI.

Hi Smacaroni thanks for looking

I would chuffed if it would rev out on the mt 50 but it won't rev above 2-3k

I think it's time for the refuse

My ambition is to get this problem done , report on the motor as I reckon I will be an expert on xt550 engines by then , and then post a picture on the site so you guys can see Frankenstein's monster in all it's glory

What day reckon ?

Oh, yeah, the XT550 is no screamer, but 2-3K it's just getting up to speed.


Look up the Transmic CDI for 12 degrees, it's simple (for someone who isn't a clumsy oaf with solder like me), cheap and functional. I can attest to the last two having run it for about 200 miles.

So the latest

the guy at electrex world who supplied the new cdi unit suggested that the stator may be faulty as in his opinion the xt550 electrics fail generally in the order cdi / stator / pulsar coil . He thought the stator might power the mt50 cdi but not the xt which requires more power

Having replaced the ht coil and the cdi with new parts the stator was suspected.

Aparrently even if the resistance between the red and brown wire shows as being in spec , the way to further test is to check resistance with a hot engine. If the stator is serviceable the resistance reading will go up . If the resistance reading goes down with the hot engine the stator could be failing.

I set up the mt 50 cdi checked red to brown cold at 194 ohms and started the engine. Once hot checked again ....274 ohms diminishing as the engine cooled.

Don't suppose any one has any other ideas .?

Still trying to figure this non spark problem out! One thing that sprung to mind was that when i checked continuity between the brown wire from the stator and ground i got continuity. AND when i checked from the red wire to ground I got continuity

Would some one with an xt550 check this out on their bike to see if this is correct ?


many thanks

Ignition problem solved

A leak to ground on the stator from both red and brown caused the issue even though the bike would run on an mt50 cdi.

In conclusion

When I obtained the engine the stator was not providing power to the cdi (due to the leak to earth)

It would start the engine but not rev out

Then the stock CDI failed

the bike would run on an MT 50 cdi but would not rev out

I replaced the XT CDI

Now that the stator has been repaired the engine runs fine (full revs blasting)

The point is the manual resistance readings can be achieved but no leak to earth from rd or brown can be tolerated.

Also worth noting from what I have learnt is that the carbs were changed during model swaps and all of the fuel ways noted in the J manual do not exist on a K carb !

I intend to finish the project now and post pics of the finished job

Worth bearing in mind that these engines are tolerant to change as this engine now runs well with a shorty 2 int 1 exhaust and with home made 1 into 2 air filter to carb manifold and a home made primary carb to inlet manifold ( as I was not paying £60 for a second hand one )

Big thanks to all friends from across the pond ! As this process would have been very difficult without your help

Congrats! It's a great machine, darn shame they only made 'em for two years. IMHO, the latter carb is more desirable than the early one, but as long as it runs, it's all good.


How did you repair the stator? Rewind? Add some insulators to the mounting bolts?

The stator was sent for repair

It was not re wound in its entirety however the red and brown wires were replacd and re insulated

Could you help me with a further detail for my engine

Out of the cylinder head there is a breather pipe . What is this pipe made of as it needs to be very heat resistant, where does it vent to? does it go Baku t the air box? Also the breather out of tithe top of the gearbox is that a metal pipe ? Does that go to the air box also?

The transmission/crankcase breather goes back to the air box IIRC. This does two things, first any gas blow-by is fed back into the engine and burned, this is better for the environment. This opening needs to be there to allow the pressure pulses from the piston moving up and down. Second, if you should happen to dump the bike long enough for oil to go out the breather, the oil will be caught instead of pouring out of the cases all and making a mess and perhaps making the foot pegs or tires slippery.


I don't recall one out of the cylinder head, but I wouldn't be surprised if it's a modern rubber substitute like Neoprene or Silicone. I'm not saying it's not there, I just don't remember.

The hose in the rocker cover goes back to the oil tank. It runs up to the backbone and the snakes its way down to the top of the tank.

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